Composer. Known through references by the theorists Anonymous IV and Johannes de Garlandia (both mid-13th century). These men described his accomplishments, and Anonymous IV also named a few compositions. Thus, although no musical sources include attributions to Pérotin, it is possible to identify a small number of his works. He is said to have revised the Magnus Liberof Léonin, both abbreviating it and writing improved clausulas. He also wrote 3- and 4-voiced organum,a major advance over the earlier 2-voiced organum.In fact, Anonymous IV singles out tile 4-voiced Viderunt onmesand Sederunt principesand the 3-voiced Alleluia, Pascha nostrumand Alleluia, Posui adiutorium.The theorist also ascribes to him three conducti.A number of other 3-voiced organaand some clausulaecan be attributed to him on stylistic grounds. In addition, a set of about 150 short clausulaeclearly suit the purpose of abbreviating the Magnus Liber.Thus, the total number of pieces that are possibly by Pérotin is large; the attributions are far from solid, however. For the most part we cannot be sure exactly which extant compositions are his.